Coating liquids that contain ultrafine particles of inorganic compounds, for example zinc oxide, in water are known. However, ultrafine particles of zinc oxide (hereinafter, also ultrafine zinc oxide particles) generally have poor dispersibility in water. Consequently, the application of such coating liquids results in layers that have uneven concentrations of ultrafine zinc oxide particles.
There have been disclosed gas barrier films that are formed by applying a coating liquid containing a polyvalent metal compound such as zinc oxide on a layer containing polyacrylic acid (see for example Patent Literatures 1 and 2).
Patent Literature 1 describes that when water is used as a solvent for the coating liquid containing a polyvalent metal compound, the application of the coating liquid to a polycarboxylic acid polymer layer results in a reaction between the polycarboxylic acid polymer and the polyvalent metal compound possibly to form an inhomogeneous precipitate. The literature then describes that nonaqueous solvents or mixtures of nonaqueous solvents and water are preferable as the solvents for the coating liquids. However, the nonuse of organic solvents has been desired recently from the environmentally friendly point of view. That is, coating liquids containing water as the solvent are desirable.
Patent Literature 2 describes that the coating liquid containing a polyvalent metal compound is applied to a polycarboxylic acid polymer layer that has improved water resistance, and therefore the coating liquid can use water as a solvent.
However, Patent Literatures 1 and 2 do not fully consider components other than the polyvalent metal compounds that may be contained in the coating liquids or do not study sufficiently the dispersibility of the polyvalent metal compounds.